Electric valve protective system



pt. 26, 1939. H. WINOGRAD 2,174,432

, ELECTRIC VALVE PROTECTIVE SYSTEI Filed Nov. 21, 1936 Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE ELECTRIC VALVE PROTECTIVE SYSTEM Application November 21, 1936, Serial No. 111,991

3 Claims.

This invention relates in general to improvements in electric valve protective systems, and more particularly to a system for impressing a negative potential on a control electrode of an electric valve for causing interruption of the flow of current through the valve upon occurrence of a disturbance in the operation thereof.

Electric valves utilized in electric translating systems are frequently provided with control electrodes on which suitable potentials may be impressed for controlling the operation of the valves. The control electrode of a valve may be brought to a negative potential with respect to the cathode potential to cause interruption of the flow of current through the valve, such operation being efiected either manually or automatically in response to the occurrence of a disturbance in the valve or in the circuits associated therewith. In valves which are intermittently conductive during normal operation, the control electrodes are preferably energized from a source of alternating current through a control transformer. It is then advantageous to render the control electrodes negative with respect to the associated cathodes by short circuiting the transformer to suppress the action thereof and substituting therefor a source of direct current, or to bridge the transformer with rectifying means impressing a negative potential on the control electrodes 30 of the valves and simultaneously causing the voltage of the transformer to be reduced.

It is, however, preferable to connect the control transformer with the alternating current source through a transformer connected with rectifying means which cause the impression of a negative potential on the control electrode of the valve upon short circuiting of the control transformer. The rectifying means may consist of vapor valves which may be arranged to normally carry a small current under a low voltage to maintain such valves continuously ionized without subjecting them to rapid deterioration.

It is, accordingly, one object of the present invention to provide a protective system for an electric valve having a control electrode, in which the valve may be rendered non-conductive by completely short circuiting a control electrode transformer associated therewith.

Another object of the present invention is to provide a protective system for an electric valve having a control electrode in which short circuiting of a control transformer causes the impression of a negative potential on the control electrode of the valve.

Objects and advantages other than those abQVQ set forth will be apparent from the following description when read in connection with the accompanying drawing which diagrammatically illustrates one embodiment of the invention applied to the control of a plurality of electric valves forming part of an alternating current rectifying system.

Referring more particularly to the drawing by characters of reference, reference numeral 6 designates a source of alternating current such as an alternating current line or circuit connected with a suitable alternating current generator (not shown). Line 6 is to be connected with a direct current line or circuit 1 through a translating system comprising one or more electric valves generally designated by 8. When a plurality of valves are utilized, such valves are severally provided with anodes 9 preferably arranged within a common casing, the cathodes of the valves being combined to form a single cathode structure ll. Suitable means are provided for bringing cathode H into electron emitting condition and for maintaining the cathode in such condition, such means being well known and therefore not shown. Anodes 9 are severally connected with the conductors of line 6 through the phase portions of a transformer I2 which may be replaced by a plurality of single phase transformers, and through the contacts of a switch 13. One conductor of line I is connected with cathode H, and the other conductor of the line is connected with the secondary windings of transformer l2 either directly or through an interphase transformer [4.

The conductivity of each valve may be controlled by means including control electrodes I6 severally associated with anodes 9 and each arranged in or about the path of the discharge occurring between the associated anode and cathode II. It will be assumed that valves 8 are of the discontinuously controllable vapor type, and that each control electrode may accordingly prevent the flow of current through the associated anode when the control electrode is at a negative potential and may release such flow of current when the control electrode is at a positive potential, the potential of cathode l I being taken as datum for the several control electrode potentials. Each control electrode I6 is connected with the cathode ll through a circuit comprising a current limiting resistor l1 and one of the phase portions of the secondary Winding l8 of a control transformer [9 having a primary winding 2i energized from line 6. Winding I8 is connected in star to form a neutral point which is connected with cathode ll through a resistor 22. Resistor 22 may be serially connected with means for producing a variable unidirectional voltage such as a voltage divider 23 receiving current from a direct current source such as a generator 24.

Valves 8 may be rendered non-conductive by means including a transformer 26 having a primary winding 2'5 comprising a plurality of phase portions severally connecting the phase portions of winding 2!! with line 6. It will be understood that transformer 26 may also be replaced by a plurality of single phase transformers if desired. The phase portions of winding 22 may be connected in parallel with suitable impedance means such as resistors 29, if winding 22 is normally to carry a current of lower magnitude than the normal current of winding 2!. A plurality of electric valves 3| connect winding 28 with resistor 22 for the supply of rectified current thereto. Valves 35 are preferably of the two electrode vapor type, each provided with a thermionic cathode maintained in electron emitting condition by means of a heating transformer 32.

Means are provided for controlling the flow of current between line 6 and resistor 22 by way of transformer 26 and valves 3i, such means comprising a fast acting relay 33 having contacts for establishing a short circuit across terminals of transformer 59 to cause impression of the full voltage of line 6 on winding 22. Although relay 33 may be arranged to short circuit winding it, it is generally preferred to cause the relay to short circuit winding 2! which presents a lower number of terminals. Relay 33 is rendered responsive to an operating condition of valve 8, such as the magnitude of the flow of current through the valve, by connecting the coil of the relay with suitable current responsive means such as a current transformer 34 inserted in one of the connections between line 6 and transformer l2. Another current transformer 35 is inserted in one of the conductors joining resistors 29 with the contacts of relay 33, and is therefore responsive to the flow of current through the contacts of relay 33. The secondary winding of current transformer 36 is connected in parallel with the secondary winding of current transformer 34 to cause relay 33 to maintain the contacts thereof closed after the coil of relay 33 ceases to receive current from current transformer 36. It is generally preferable to provide a second relay 3'! of the slowly acting type, provided, if desired, with a time delay device, and to have contacts 33 connected with resistors 29 for diverting the flow of current from the contacts of relay 33. The coil of relay 37 is connected across one of resisters 29 and current transformer 55 through contacts as of switch l3. Relay 3? may also be provided with contacts ll connecting the trip coil of switch is with a current source, such as a battery 42, for causing opening of switch 03 upon operation of the relay, Contacts ll may also be arranged on relay 33 if desired.

In operation, line 6 being energized and switch l3 being closed, anodes ii are sequentially brought to a positive potential with respect to the potential of cathode H and are thus sequentially caused to carry current, the successive anode current impulses combining at cathode El to form a flow of direct current supplied to line 2 as is well known in the art. If it is not desired to utilize control electrodes it to regulate the voltage of line 2, generator 24 and voltage divider 23 may be omitted, and the connections between control electrodes l6 and winding [8 are then so arranged that each control electrode becomes positive with respect to cathode II at the same moment of the voltage cycle of line 6 as anode 9, or at an earlier moment. If it is desired to vary the moments of initiation of the flow of current through each anode to regulate the voltage of line I, such result is obtained by so connecting the control electrodes with winding l8 and so selecting the voltage of generator 24 that the moment at which each control electrode be comes positive may be varied within the normal operating period of the associated anode by adjustment of the taps of voltage divider 23. Control electrodes l6 also operate as anodes and carry current impulses which combine at cathode M to form a unidirectional current flowing through voltage divider 23 and through resistor 22, thereby causing the occurrence of a unidirectional voltage drop in the resistor.

During such operation, winding 21 receives a predetermined portion of the current of winding 25, or the entire current thereof if resistors 29 are omitted. Winding 27 is thus energized under a voltage which is a small fraction of the voltage of line 5, and induces in winding 28 another voltage which is rectified by valves 3| and is impressed on resistor 22. If such voltage is at the most equal to the voltage drop produced in resistor 22 by the current of control electrodes l6, valves 3i will not carry any current and will therefore have no effect on the normal operation of control electrode Hi. It is, however, preferable to so adjust the values of resistors 22 and 29 that valves 3| continuously apply a small current to resistor 22, thus causing the appearance in resistor 22 of an additional voltage drop which may be neutralized by adjustment of voltage divider 23. In such manner, the vapor within valves Si is continuously maintained in ionized condition so that the valves are always in the most favorable condition for functioning, as described hereinafter, upon operation of relay 33. Although valves 3| are thus required to carry current continuously, such current is of such intensity and voltage as not to materially reduce the life of the valves. The currents normally flowing through the coils of relays 33 and 3! are of insufiicient magnitudes to cause operation of the relays.

Upon occurrence of a disturbance in the system, such as a short circuit in line I or a backfire in one of valves 8, a flow of current of abnormal magnitude takes place between line 6 and transformer l2. Current transformer 34 supplies a current of corresponding magnitude to the coil of relay 33, thus causing the relay to close the contacts thereof. As a result of such operation, transformer I9 is short cirouited and ceases to impress alternating potentials on control electrodes it of valves 8. Another result of such operation is to impress the entire voltage of line 6 on winding 21, thus causing winding 28 and valves 3! to impress a large unidirectional voltage between the terminals of resistor 22. Such voltage is chosen of such sign and polarity as to maintain control electrodes I 6 at a negative potential with respect to the potential of cathode l I irrespective of the adjustment of voltage divider Further transfer of the flow of current from one anode 9 to another anode is thus prevented, and the flow of current through the valve 8 car rying current at the moment of operation of relay 33 ceases when the anode of such valve becomes negative with respect to cathode ll.

Valves 8 are thus all rendered non-conductive, and the flow of current between line 6 and line 1 is permanently interrupted.

Upon closure of the contacts of relay 33, current transformer 36 receives the current flowing through one of the contacts of the relay, and a corresponding current is supplied from the secondary winding of current transformer 36 to the coil of relay 33 to cause the relay to maintain the contacts thereof closed even after current transformer 24 ceases to carry current. Operation of relay 33 also causes the coil of relay 3! to be energized at the voltage of line 6, and relay 3'! closes the contacts thereof. Contacts 38 divert the flow of current from the contacts of relay 33 and from current transformer 36 so that the coil of relay 33 becomes deenergized and the relay returns to the position shown wthout interrupting any current at the contacts thereof. Contacts 4| complete the tripping circuit of switch l3 which is thus caused to disconnect transformer l2 from line 6 and to open contacts 39. The coil of relay 3'! is thus deenergized and relay 31 returns to the position shown. The entire system is then as shown on the drawing and the flow of current through valve 8 may be reestablished by reclosing switch l3 after the cause of the disturbance has been removed.

It will be observed that the contacts of relay 33 are only required to close the circuit thereof for a very short period of time and to thereafter open without breaking any current. The relay may therefore be provided with light contacts and may be of light construction permitting operation thereof in a fraction of a cycle of the voltage of line 6. Thus contacts are never subject to arcing and are therefore always in proper condition for carrying current immediately upon closure thereof.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In an electric translating system, an electric valve having an anode and a cathode, means for controlling the conductivity of said valve including a control electrode associated with said ode and a source of alternating current, a transformer connected with said control electrode and a resistor connecting said transformer with said cathode, and means for rendering said valve non-- conductive including a transformer having a primary winding connecting the first said transformer with said source and having a secondary winding divided into a plurality of phase displaced portions, a plurality of electric valves severally connecting said secondary winding portions with said resistor for the supply of uninterrupted rectified current thereto, a relay operable responsive to an operating condition of the first said valve having contacts for establishing a short circuit across terminals of the first said transformer, and a relay operable responsive to the fiow of current through the said contacts for diverting the fiow of current from the said contacts.

2. In an electric translating system, an electric valve having an anode and a cathode, means for controlling the conductivity of said valveincluding a control electrode associated with said anode and a source of alternating current, atransformer connected with said control electrode and a resistor connecting said transformer with said cathode, and means for rendering said valve non-conductive including a transformer having a primary winding connecting the first said transformer with said source and having a secondary winding divided into a plurality of phase displaced portions, a plurality of electric valves severally connecting said secondary winding portions with said resistor for the supply of uninterrupted rectified current thereto, a relay operable responsive to an operating condition of the first said valve having contacts for establishing a short circuit across terminals of the first said transformer, means responsive to the flow of current through the said contacts to cause said relay to maintain said contacts closed, and a relay operable responsive to the flow of current through the said contacts for diverting the flow of current from the said contacts.

3. In an electric translating system, an electric valve having an anode and a cathode, a switch serially connected with said valve for controlling the flow of current therethrough, means for controlling the conductivity of said valve including a control electrode associated with said anode and a source of alternating current, a transformer connected with said control electrode, a resistor connecting said transformer with said cathode, and means for rendering said valve non-conductive including a transformer having a primary winding connecting the first said transformer with said source having a secondary winding divided into a plurality of phase displaced portions, a plurality of electric valves connecting said secondary winding with said resistor for the supply of uninterrupted rectified current thereto, a relay having contacts for establishing a short circuit across terminals of the first said transformer, and means controlled by said relay for causing opening of said switch, and means comprising an element of said switch for controlling the third said means.

HAROLD WINOGRAD. 

